This invention relates to ionic junctions for use in radiation detectors, and more particularly to ionic junctions with greatly decreased ionic dark currents.
Radiation detectors based on thallium halides (e.g. TlBr) have in the past several years begun to live up to expectations and have demonstrated ever superior performance given their high stopping power (˜280 g/mol mol. wt.), high dark resistivity (Eg˜2.7 eV, ρ>1010 Ωcm), good resolution (2% at 662 keV), and increasingly high μτ products ((μτ)e>2×10−3 cm2/V), the latter resulting from improvements in the growth of large high quality single crystals by vertical Bridgman and zone refining methods. However, due to the ionic nature of the dark conductivity, under high dc fields, one finds evidence for long term degradation due to electrochemical decomposition and/or large polarization at/near the electrodes resulting from the dark, ionic current.
We have previously developed a detailed predictive model which enables one to select dopants to maximize the dark resistivity as well as minimizing the contribution of the thallium ion to the dark current believed to control the degradation rate. Nevertheless, even with a room temperature resistivity of >1010 ohm-cm, long term degradation due to electromigration of ions still remains a challenge.